1. Field of the Invention
This invention relates generally to a method for determining estimated vehicle dynamics parameters and, more particularly, to a method for determining estimated vehicle dynamics parameters that employs a vehicle parameter estimator, a vehicle condition detector and a rich steering input detector for providing an estimated vehicle understeer coefficient, front cornering compliance and rear cornering compliance in real time.
2. Discussion of the Related Art
Vehicles are designed so that the vehicle handling response complies with certain design specifications. Vehicle dynamic parameters define the vehicle handling response, and therefore, nominal parameters define a nominal vehicle handling response. The vehicle dynamic parameters of understeer coefficient, front cornering compliance and rear cornering compliance are the most dominant dynamic parameters for determining the stability and dynamic handling behavior of a vehicle. The understeer coefficient defines the vehicle yaw rate or turning radius for a particular steering angle. The front cornering compliance and the rear cornering compliance define the distribution of the side-slip to the front and rear axle when the vehicle is turning. The cornering compliances include the ratio defined by the steering angle and the lateral force of the wheels. These parameters vary according to different vehicle loading, tire pressure, tire wear, and vehicle-to-vehicle variations of suspension characteristics, etc.
Parameter deviations from the nominal values may cause performance degradation of the chassis/vehicle control systems. For example, as the vehicle ages, the various dynamic parameters change, resulting in a change in the turning radius of the vehicle in response to the same steering angle. It would be desirable to monitor the vehicle dynamic parameters to determine if a problem exists so that suitable steps could be taken. The theory of real-time estimation of a dynamic system is known, and there have been several attempts to estimate vehicle dynamic parameters. The known theories are not feasible enough to be applied to a real vehicle system because they do not properly account for the issues of non-linearity and input richness. These issues can be resolved and the estimation algorithm can be improved.